Field of the Invention
The present invention relates to a metal substrate for use as the substrate for a fixing member for use in a fixing assembly of an electrophotographic image forming apparatus, in particular, a metal substrate for use as the substrate for a fixing member which effectively prevents the breakage or damage of the fixing member, and a fixing member and a fixing assembly which use the metal substrate.
Description of the Related Art
An electrophotographic image forming apparatus includes a heat fixing assembly which employs a belt heating system for reducing power consumption. FIG. 2 is a cross sectional view of a heat fixing assembly illustrating a skeleton framework of a typical belt heating system. The heat fixing assembly includes a fixing belt 11 as a fixing member in an endless form, a pressure roller 20 as a pressure member disposed opposite to the fixing member, and a ceramic heater 12 as a heating means disposed in contact with the inner peripheral surface of the fixing belt. The fixing belt 11 and the pressure roller 20 form a fixing nip N. A recording material 30 on which an unfixed toner image T is formed and supported is introduced in the fixing nip part N. The toner is fused so that the toner image is fixed on the recording material 30.
FIG. 3 is a cross sectional view illustrating a fixing belt 11. The fixing belt 11 mainly includes 3 layers including a substrate 101, an elastic layer 102, and a surface layer 103 such as a releasing layer in this order from the side of a ceramic heater 12. A thin metal seamless belt having high thermal conductivity is used as the substrate 101.
In order to obtain a satisfactory fixed image in such a belt heating system, it is necessary to stably form a sufficient fixing nip part N. Accordingly, the fixing belt 11 for use is slid on the ceramic heater 12 under approximately uniform pressure between the ceramic heater and the pressure roller 20 along the longitudinal direction, i.e. the axial direction of the cylindrical fixing belt.
The fixing belt 11 in such a use may be subject to scratching and the development of perforations due to pressure applied to a small region, when fine foreign matter such as dust and sand intrude into the interior of the main unit so as to be held between the ceramic heater 12 and the substrate 101 in the fixing nip part N. The occurrence of scratching and perforations may cause breakage of the fixing belt 11 during repeated use, thus being the cause of the breakage.
According to a proposal in Japanese Patent Application Laid-Open No. 2010-54821, the surface of a ceramic heater in contact with a fixing belt is provided with a bump inside the end of the fixing belt in the longitudinal direction so as to prevent the dust and sand from intruding into the interior.
For further reduction in power consumption, thinning of a fixing member, in particular, thinning of a metal substrate, is required. When the metal substrate for a fixing belt is thinned to, for example, 30 μm or less, the occurrence of fracture and dents is predicted at the bump provided on the surface of a ceramic heater described in the Japanese Patent Application Laid-Open No. 2010-54821.
The present inventor recognizes that in the fixing member with a metal substrate having a thickness of 30 μm or less, the metal substrate itself needs to have more enhanced scratching resistance and perforation resistance under the pressure to be applied to a small region when invaded with fine foreign matter such as dust and sand.